1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus. In particular, the present invention relates to an ultrasonic diagnostic apparatus wherein ultrasounds are transmitted in a direction along a scan line extending within a subject and ultrasounds reflected on the respective points on the scan line are received to form received signals is sequentially repeated on a plurality of scan. Thereby, in the present invention, an image signal carrying image information on a tomographic plane formed by the plurality of scan lines inside the subject is produced on the basis of the received signals derived through those operations, and a two-dimensional image based on the image signal thus derived is displayed.
2. Description of the Related Art
Hitherto, there has been used an ultrasonic diagnostic apparatus for diagnosis of diseases of viscus inner organs or the like within a subject, and particularly, within a human. Such a device has operated by means of producing and displaying a tomographic image of the inside of the human body and a blood flow distribution image on the tomographic plane on the basis of received signals derived through transmission and reception of ultrasounds with respect to the subject.
In such an ultrasonic diagnostic system, for example, there are displayed two-dimensional images such as the above-mentioned tomographic image and blood flow distribution image, and in addition a cursor superposed on the two-dimensional images. In some case, it happens that there is a need to move the cursor on a screen through operations of a handler, for example, a track ball, a mouse and the. Such a movement is needed, for example, to select one among a plurality of scan lines appearing on the two-dimensional image, or select one among a plurality of areas which are formed on each of the plurality of scan lines in such a manner that the respective scan line is divided into a plurality of partitions.
Hereinafter, in a case where one scan line is selected from among several of scan lines, the selected scan line is referred to as a "noticed area". Each of a plurality of scan lines, which are possible to be selected in the form of the noticed area, is hereinafter referred to as a "processing unit area". On the other hand, in a case where each of a plurality of scan lines is divided into a plurality of areas, and one area is selected from among the thus divided plurality of areas, the selected area is referred to as a "noticed area", and each of a plurality of areas, which are possible to be selected as the noticed area, is referred to as a "processing unit area".
As a case in which it is necessary to designate a noticed area from among a plurality of processing unit areas, for example, there are considered the following cases. One is that a two-dimensional image representative of a tomographic image or a two-dimensional image representative of a blood flow distribution image is displayed, and a predetermined point (noticed area) of the displayed two-dimensional image is designated so as to observe changes with time of a blood flow in the designated noticed area. Another is that a two-dimensional image representative of a tomographic image is displayed, and one scan line (noticed area) of a plurality of scan lines constituting the two-dimensional image is designated so as to observe changes with time of a one-dimensional ultrasonic reflection intensity distribution (boundary site of internal organs or the like) in the designated noticed area (one scan line).
By the way, a plurality of scan lines on a two-dimensional image have discrete intervals between adjacent scan lines. Also in a case of setting up a plural of processing unit areas possible to be designated on one scan line as the noticed area, those plurality of processing unit areas are set up at discrete sites on the one scan line.
Consequently, when the noticed area is designated by the cursor (from among such discrete processing unit areas), as a display position of the cursor, there is permitted only a position superposed on any of the processing unit areas.
However, if the display position of the cursor is permitted to be only a position superposed on any of the processing unit areas, then this causes an intermittent movement of the cursor on a display screen. Thus the movement of the cursor is not synchronized with an operation of the handler. Thus, there arises the problem that an operator will experience a sense of incongruity. Specifically, for example, in case of a sector scan, the scan lines are close near the surface of the human body (as the subject), while the scan lines are scattered at a site the deep within the subject. In this case, when it is intended to move the cursor to another scan line, a movement of the cursor will be different, in spite of the same operation of the handler. That is, the cursor movement will differ between a case in which the cursor is located in an area corresponding to an area near the surface of the human body (as the subject) within the subject and a case in which the cursor is located within an area corresponding to an area deep within the subject. This causes an operator to experience a sense of great incongruity.